Assessment of Chemotherapy Response in Colorectal Cancer Using PET-CT Versus DWI-MRI

Evaluating therapeutic efficacy in colorectal malignancies presents significant challenges when relying solely on conventional anatomical imaging approaches. The primary aim of this prospective study was to compare the diagnostic effectiveness of integrated positron emission tomography-computed tomography (PET-CT) and diffusion-weighted magnetic resonance imaging (DWI-MRI) for monitoring chemotherapy response in patients with colorectal cancer.

This prospective comparative analysis included 132 histologically confirmed patients with colorectal cancer planned for first-line chemotherapy (FOLFOX, FOLFIRI, or CAPOX). Twelve of 132 patients left the study during follow-up. Patients underwent baseline PET-CT and DWI-MRI exams, with repeat scans at 3, 6, and 12 weeks post-treatment. Response assessment used RECIST v1.1 for morphology, PERCIST v1.0 for metabolism, and quantitative apparent diffusion coefficient (ADC) analysis for DWI-MRI. Survival outcomes, correlation studies, and receiver operating characteristic curve analysis were used.

Patients had a mean age of 62.7 ± 9.6 years, with 51.7% men. PET-CT indicated a 36.0% ± 25.3% SUVmax reduction, and DWI-MRI showed a 51.4% ± 42.1% ADC rise at 12 weeks (p < 0.001). A significant negative association (r = -0.732, p < 0.001) occurred between SUVmax and ADC values. DWI-MRI outperformed PET-CT in terms of diagnostic performance, with an AUC of 0.887 (p = 0.156), a sensitivity of 90.9% compared to 84.4%, and a specificity of 76.7% compared to 72.1%. Concordant responders demonstrated better progression-free survival (18.0 vs. 4.8 months, p < 0.001) and overall survival.

Both PET-CT and DWI-MRI demonstrate excellent diagnostic performance for assessing chemotherapy response, with DWI-MRI showing marginal superiority in sensitivity and predictive accuracy, supporting its use as a radiation-free alternative for treatment monitoring.